1. Field of the Invention
The present invention relates to powdery silica composite particles comprising a phosphonium salt ionic liquid immobilized in the surface, a process for producing the same, and a silica composite particle dispersion and a resin composition comprising the silica composite particles.
2. Description of the Related Art
Ionic liquids are salts of cations and anions. They are substances that are in liquid state at room temperature and atmospheric pressure and have no melting points. Some of them have been studied in the electrochemical field since the early years of the 20th century. However, their other applications were not studied.
During the 1990s, ionic liquids came into the limelight amidst calls for green chemistry, because of their interesting properties such as incombustibility and nonvolatility. Therefore, various ionic liquids have been developed. In recent years, ionic liquids have been studied as to their use as incombustible, nonvolatile, and highly polar solvents.
However, applications of ionic liquids other than the use as solvents still remain to be developed, and novel applications thereof are expected for the future.
One possible novel application of ionic liquids is functional materials containing an ionic liquid. However, such functional materials containing an ionic liquid must be produced by uniformly dispersing the ionic liquid in various solvents or resin materials. However, ionic liquids, which are in liquid state, are disadvantageously exceedingly difficult to uniformly disperse in various solvents or resin materials.
Therefore, the present inventors have previously proposed powdery silica composite particles comprising an ionic liquid immobilized in the surface (see Japanese Patent Laid-Open No. 2007-270124 (claims)). The powdery silica composite particles disclosed therein can be dispersed uniformly in solvents or resins.
The powdery silica composite particles disclosed in Japanese Patent Laid-Open No. 2007-270124 (claims) are obtained by: adding acid or alkali to a reactant mixture comprising: a silica sol containing core silica particles of 5 to 200 μm in average particle size; alkoxysilane; and an ionic liquid such that the alkoxysilane is hydrolyzed; and centrifuging the obtained reaction suspension to precipitate solid matter. Therefore, in most cases, the silica composite particles are disadvantageously produced at yields as low as 50% or lower and immobilize thereon a phosphonium salt ionic liquid at a content of at most 0.6% by weight in terms of the P atom thus the amount of the phosphonium salt ionic liquid immobilized cannot be large.
Accordingly, an object of the present invention is to provide highly dispersible, powdery silica composite particles comprising a phosphonium salt ionic liquid immobilized in the surface and comprising the phosphonium salt ionic liquid at a high content. Another object of the present invention is to provide an industrially advantageous process capable of producing the powdery silica composite particles at high yields.